For many quality testing and other procedures, hardness testing holds prime importance.
Hardness tests enable us to evaluate the properties of materials such as ductility, strength and wear resistance that will help us determine to check if the material is suitable for a specific purpose.
The hardness of a material is not its fundamental property, but it’s only a way to determine the resistance exhibited by material to permanent deformation.
The hardness test to be performed for a specific material is based on the homogeneity, size, type, and condition of the material you are going to test. There are several hardness tests available, and one of them is the Vickers hardness test.
Vickers hardness testing
Vickers hardness testing is a multifaceted testing method that can be used for both micro and macro hardness testing. Vickers hardness test was developed by George E. Sandland and Robert L. Smith in 1921 as an alternative to the Brinell method for measuring material hardness.
A wide range of applications and materials can be subjected to Vickers hardness testing, including microhardness testing.
It is generally considered easy to be carried out as compared to other hardness tests since the indenter can be used with all kinds of materials irrespective of their hardness and also because the size of the indenter doesn’t effect the required calculations.
Categorization of Vickers testing method
Vickers testing method is considered as a static hardness testing method that can be characterized further into the following aspects:
- Regarded as one of the standardized procedures (ASTM E384, ASTM E92, ISO 6507)
- It is an optical method which means the hardness value of a test material/specimen is determined by the size of the indentation.
- The indenter has a plane angle of 136° and is an equilateral diamond shaped pyramid.
- Vickers testing method can be used across all load ranges used for hardness testing (from micro to macro ranges) as it has a test load range from 1gf up to 120 kgf according to ASTM and 1gf according to ISO respectively.
How is it performed?
Vickers hardness test is incredible in its ability to be performed on both micro and macro hardness scales with a maximum test load of around 50 kgs.
Vickers hardness test is performed by putting a controlled force on the indenter that is usually a square-shaped diamond pyramid over a period of time.
After a particular indenter is pressed into the surface under testing, the indentation resulting from it is measured with the aid of high-powered magnifying instruments such as microscopes and eyepieces. Sometimes, the software is also used to analyze and generate more precise results.
Two varying forces are used by Vickers hardness tests such as micro ranges at 10 to 100 grams and macro ranges from 1 to 100 kgs. Both ranges use the same indenter hence producing hardness values that are constant over all-metal hardness ranges.
Sample preparations are mandatory to obtain precise results. A sample is required that is small enough to fit into the tester adequately.
Moreover, to achieve accurate measurement and regular shape of indentation, the preparation must have a smooth surface. This also makes sure that the indenter can conveniently hold the subject perpendicularly.
Specimen required for Vickers hardness testing
The surface of the specimen that is needed for the Vickers testing method needs to be prepared first when using Vickers method. This is because the requirements of specimen surface quality are stricter than other testing procedures.
The specimen needs to meet the given requirements for Vickers hardness test:
- The specimen/ material has to be precision-ground in case of macro-hardness testing or polished for micro-hardness testing.
- The specimen/material shouldn’t move during the testing procedure and should be clamped strongly.
Moreover, care should be taken regarding any kind of vibration or disturbance while conducting a Vickers hardness test to avoid poor results.
Importance of Vickers hardness test
Vickers test can be very beneficial for applications such as testing ultra-thin materials like foils.
They can also be very useful for measuring single microstructures, small parts or surfaces and determining a hardness change profile by producing an indentation series.
If the indentation is smaller, the object will be harder. Likewise, the material is expected to lack hardness if the indentation is large.
Vickers hardness testing is used by several industries to determine the right kind of material to be used for machinery and operations. The material with the best hardness conditions is then chosen for the specific purpose in the industry.
Advantages of Vickers hardness tests
There are several advantages of the Vickers hardness test. Some of them are discussed below:
- Vickers hardness tests procedures cover the entire hardness range, and hence it can be used for any kind of specimen or material whether it’s hard or soft. Either it’s about microhardness testing or macro hardness testing, Vickers hardness tests can generate accurate results for both.
- Often considered as Microhardness testing, Vickers hardness tests are used to test any kind of material including composites, ceramics, and metals, etc.
- Only one type of indenter is used for various kinds of Vickers methods.
- The specimen used in the Vickers hardness test can be used for other purposes as well because the test also accompanies non-destructive testing.
Disadvantages of Vickers hardness testing
Despite many advantages that render Vickers testing to be one of the best hardness testing methods, there are a few disadvantages as well that should be taken into consideration.
- As the indent is measured optically, the specimen’s surface quality must be smooth and good. This means that the precise evaluation could be difficult if the test location is not well- prepared (i.e., polished and ground).
- Compared to Rockwell hardness testing and other methods, Vickers hardness testing is comparatively slow. The test cycle doesn’t include the time taken to prepare the specimen and takes around 30-60 seconds approximately.
- Vickers hardness tests need to be equipped with an optical system due to the necessary optical indent evaluation. This renders Vickers hardness testing to be more expensive to purchase as compared to other testers, including Rockwell tester.